As you said, Bootstrap-like frameworks are a good alternative when you don't have a designer in the project or even when you don't have time to create a styleguide properly.
After thinking a lot about the need of those big CSS frameworks in my projects, these ones crossed my path:
As a front-ender, I love to create the styles and optimize it until it breaks. Excluding Bulma and Primer, the above are considered micro-frameworks or even CSS starter packs; and they helped me to save time while developing.
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